1. Field of the Invention
The present invention relates to a device and a method each of performing a switching control to a standby system in a hybrid system of a duplex system and a backup line.
2. Description of the Prior Art
FIG. 13 is a block diagram showing a hybrid system including a duplex system using a packet exchange and a backup line using a public network. Referring to FIG. 13, numeral 110 represents a first packet exchange. The first packet exchange 110 exchanges frame information (packets). The first packet exchange 110 is constituted of a communication line management processor (MPR) 111, and a pair of a communication multiplexer (CMU 0 system) 112 and a communication multiplexer (CMU 1 system) 113.
The communication line management processor 111 can continue communication by processing data desirably when a transfer occurs between duplex lines.
The pair of communication multiplexers 112 and 113 are connected via different lines, respectively. Line control devices (LC) 114 and 115 are built in the communication multiplexers 112 and 113, respectively.
Numeral 120 represents a second packet exchange. The second packet exchange 120 can exchange frame information (packet), like the first packet exchange 110. The second packet exchange 120 can switch the line to the line via the first packet exchange 110 or the backup line (public network) 160.
Numeral 130 represents a third packet exchange. The third packet exchange 130 can exchange frame information (packet), like the first packet exchange 110. The third packet exchange 130 interchanges the line to the public network 160 or the host 140.
Numeral 140 represents a host. The host 140 transmits desired information in response to a request from the terminal 150. The host 140 is constituted of a CPU, a memory, and other elements. Hence a user can perform a desired communication via the terminal 150.
In such a configuration shown in FIG. 13, the hybrid system including a duplex system using a packet exchange and the backup line 160 using a public network operates in accordance with the signals shown in FIG. 14.
With a communication via the line for the communication multiplexer (CMU 0 system) 112, when the line is transferred to the communication multiplexer (CMU 1 system) 113 (refer to (1) in FIG. 14), the communication line management processor 111 requests the line control device (LC) 114 in the communication multiplexer (CMU 0 system) 112 to perform a transmission queue sweeping operation. The line control device (LC) 114 under the sweeping request outputs a transmission regulation signal frame (RNR, P frame signal) to the opposite station (the second packet exchange 120) to regulate transmission from the opposite station (the second packet exchange 120) and to verify the serial transmission number of an I-frame including data (refer to (2) in FIG. 14).
The opposite station (the second packet exchange 120), which has received the transmission regulation frame, outputs the response (RR, F-frame signal) of a normal notification signal to the line control device (LC) 114 in the communication multiplxer (CMU 0 system) 112. The line control device 114 notifies the communication line management processor 111 of the transfer data communication (refer to (3) in FIG. 14).
That is, the communication multiplexer (CMU 0 system) 112 notifies the processor 111 of the transmission serial number in a transmission waiting state before a switching operation to resume the communication.
The communication line management processor 111 notifies the line control device (LC) 115 in the communication multiplexer (CMU 1 system) 113 of transfer data to reopen the transmission (refer to (5) in FIG. 14) after the communication multiplexer (CMU 0 system) 112 (refer to (4) in FIG. 14) has swept away the transmission queue.
Thereafter, the communication multiplexer (CMU 1 system) 113, which has received the transfer data notification, reopens to accumulate the transmission queue frame corresponding to the event number from the processor 111. The communication multiplexer (CMU 1 system) 113 outputs a command (PR. P frame signal) for a normal notification signal to the opposite station (the second packet exchange 120) (refer to (6) in FIG. 14).
When the communication multiplexer (CMU 1 system) 113 receives a response signal (PR. F frame signal) from the opposite station (the second packet exchange 120) in response to the normal notification signal (PR. P frame signal), the normal communication is reopened (refer to (7) in FIG. 14).
In the hybrid system where the duplex system uses the packet exchange and the backup line uses the public network, the communication line is connected to the backup line with the public line in the following five cases: (1) a transit line trouble (an abnormal signal line, an abnormal data link, a LC trouble, and the like), (2) a line closed due to a command, (3) a RNR frame received, (4) an LC congestion, and (5) an abnormal queue length regulation value of a transmission queue per route.
Regarding the hybrid system including the duplex system using the packet exchange and the backup line using the public network shown in FIG. 13, an explanation will be made as for the communication network structure using a basic communication line and the network structure where a line is switched to the backup line with the public network 160, with reference to FIGS. 15 and 16.
FIGS. 15 and 16 show more in detail the hybrid system including the duplex system shown in FIG. 13 and the backup line using the public network.
The line management processor 111 in the first packet exchange 110 includes a processing unit 111a in the layer 3, a line management unit 111b and a backup control unit 111c.
The line control device 112 includes the processing unit 112a in the layer 1 (L1), a processing unit 112b in the layer 2 (L2), and a operation management unit (not shown). The line control device 113 has the same structure as the line control device 112.
Likewise, the line management processor 121 in the second packet exchange 120 includes a processing unit 121a in a layer 3 (L3), a line management unit 121b, and the backup control unit 121c. The line management processor 131 in the second packet exchange 130 includes a processing unit 131a in a layer 3 (L3), a line management unit 131b, and the backup control unit 131c. The line control device 122 includes a processing unit 122a in the layer 1 and a processing unit 122b in the layer 2. The line control device 132 includes a processing unit 132a in the layer 1 and a processing unit 132b in the layer 2.
The line control device 113 has the same structure as the line control device 112. The line control device 123 has the same structure as the line control device 122.
The host 140 includes a processing unit 140a in the layer 1, a processing unit 140b in a layer 2, the processing unit 140c in the layer 3, and a application processing unit (APL) 140d as a user program.
The terminal 150 includes a processing unit 150a in the layer 1, a processing unit 150b in the layer 2, a processing unit 150c in the layer 3, and a application processing unit 150d as a user program.
In the case of the above architecture using the basic telecommunication line, a communication is performed in the network configuration where the processing units (shaded) are linked to one another as shown in FIG. 15. When the line is switched to the backup line using the public network 160, a communication is performed in the network configuration where the processing units (shaded) are linked to one another as shown in FIG. 16.
When the RNR is received as described in the case (3), the signals are interchanged in the system, as shown in FIG. 17 or FIG. 18 to switch the communication to the backup line using the public network.
That is, the operation management unit 112 in the line control device of the first packet exchange 110 detects the congestion state. Then the processing unit 112b in the layer 2 outputs the RNR. P signal to the second packet exchange 120 via the processing unit 112a in the layer 1 (refer to (a) in FIG. 17).
In the second packet exchange 120, the processing unit 122b in the layer 2 of the line control device 122 receives the RNR. P signal from the processing unit 112b in the layer 2 (refer to (b) in FIG. 17).
Then, the processing unit 122b in the layer 2 produces a signal notifying that the opposite station is in busy, or "opposite station busy signal", to the line control unit 121b in the line management processor 121 (refer to (c) in FIG. 17).
In response to the "opposite station busy signal", the line management unit 121b produces a signal notifying that a trouble has occurred in the transit line, or "transit line trouble signal", to the backup control unit 121c (refer to (d) in FIG. 17).
When receiving a control signal from the backup control unit 121c (refer to (e) in FIG. 17), the line management unit 121b outputs a signal requesting a backup connection, or "backup connection request signal" to the processing unit 122b in the layer 2 (refer to (f) in FIGS. 17 and 18).
Next, the processing unit 122b in the layer 2 outputs a control signal that makes on the signal lines ER, RS, and the like to the processing unit 122a in the layer 1 (refer to (g) in FIG. 18).
The processing unit 122a in the layer 1 outputs the status signal every time each signal line is established (or becomes an on state) (refer to (h) in FIG. 18). After all the signal lines have been established, the SABM signal is transmitted to the third packet exchange 130 (refer to (i) in FIGS. 17 and 18).
In response to the SABM signal, the third packet exchange 130 executes a backup connection process (refer to (j) in FIGS. 17 and 18) while transmits an UA signal acting as a response signal to the SABM signal to the second packet exchange 120 (refer to (k) in FIGS. 17 and 18).
Thereafter, in the second packet exchange 120, the processing unit 122b in the layer 2 in the line control device 122 receives the UA signal and then outputs a "backup connection completion signal" being a signal notifying that the backup connection has been completed to the line control unit 121b in the line management processor 121 (refer to (1) in FIGS. 17 and 18).
The line management unit 121b notifies the backup control unit 121c of the backup connection completion (refer to (m) in FIGS. 17 and 18) while it outputs a "line open signal" acting as a signal notifying the processing unit 121a in the layer 3 of a communication reopen (refer to (n) in FIGS. 17 and 18).
Then the processing unit 121a in the layer 3 communicates using the backup line (refer to (o) in FIGS. 17 and 18).
As described above, in the five cases in each of which the communication line is connected to the backup line using the public network, the backup line communication interchanges the control signal between the second packet exchange 120 and the third packet exchange 130, as shown in FIG. 18.
As described above, even when the line in the first packet exchange is switched, the RNR frame is received so that the line is temporarily connected to the backup line. Therefore there is a disadvantage in that an extra charge is imposed while the communication line is being connected to the backup line using the public network.